Unveiling the Monoamine Oxidase Inhibitory Potential of Natural Flavonoids: A Computational Approach

 

Zakiya Fathima C, Jainey P. James*, Vaishnavi Gatty, Sindhu T.J, Akito Sheqi

Department of Pharmaceutical Chemistry, NGSM Institute of Pharmaceutical Sciences (NGSMIPS),

Nitte (Deemed to be University), Deralakatte, Mangaluru - 575018, Karnataka, India.

 

ABSTRACT:

Flavonoids, a group of polyphenolic compounds widely present in plants, are recognised as secondary metabolites with wide range of biological activity. This study aimed to assess the potential of flavonoids to inhibit monoamine oxidase (MAO) using in silico tools. The investigation involved evaluating the physicochemical, pharmacokinetic, bioactivity, and toxicity parameters of the compounds through QikProp, Molinspiration, and Pro-Tox-II. Additionally, binding affinity against MAO-A and MAO-B was assessed by molecular docking study using Schrödinger software. The binding free energy of the complex was determined using Prime MMGBSA. The flavonoids met Lipinski's rule of five, demonstrating favourable physicochemical properties, and making them potential drug candidates. Most compounds exhibited positive bioactivity scores and low toxicity levels. The docking study revealed that Genistein 8-C-glucoside displayed promising multi-targeting capabilities against both MAO-A and MAO-B.  This data not only advances the understanding of flavonoid pharmacology, also serves as a key tool for future investigations into the diverse biological actions of these plant-derived compounds.

 

 

INTRODUCTION: 

Flavonoids are a diverse group of polyphenolic compounds found in various plant-based foods¹. They serve a variety of crucial roles in plants, such as inviting pollinator insects, preventing environmental stressors such as microbial infection, and controlling cell division. It appears that their chemical makeup has a significant impact on both their bioavailability and biological activity in humans². Due to the possibility that diets high in fruits and vegetables will have health benefits, there has been a surge in interest in dietary flavonoids since the 1990s³. Also, have been studied for their potential health benefits, including antioxidant⁴, anti-inflammatory⁵, and neuroprotective properties⁶.

 

 

The outer mitochondrial membrane enzymes monoamine oxidases (MAOs) catalyse the oxidative deamination of several different neurotransmitters. Hydrogen peroxide (H₂O₂) is produced as a result of oxidative deamination, which is catalysed by MAO⁷. Various reactive oxygen species have sufficient harmful reactivity to cause relevant health issues, including damage to the nervous system. It has also been shown that MAO-mediated H₂O₂ production is a cytotoxic agent implicated in oxidative stress, leading to nigral cell degeneration in Parkinson's disease (PD)⁸. Based on its sensitivity to specific substrates and modulators, MAO is found in the human brain in two isoforms, MAO-A and MAO-B. Both MAO-A and MAO-B have been proposed as targets for novel antidepressants and anxiolytics, as well as for neurodegenerative illnesses including PD and Alzheimer's disease (AD)⁹.

 

Consequently, there has been more discussion in recent years about the inhibitory effects of natural products on MAOs, particularly phenolic compounds. Some studies suggest that certain flavonoids may have the ability to inhibit MAO-B activity. Quercetin, a flavonoid found in apples, onions, and other fruits and vegetables, has been investigated for its potential MAO-B inhibitory effects¹⁰. Other flavonoids, such as kaempferol and luteolin, have also shown inhibitory activity against MAO-B in experimental studies¹¹. The mechanisms by which flavonoids exert their MAO-B inhibitory effects are not fully understood, but it is believed that they may act by binding to the enzyme and interfering with its activity. Additionally, the antioxidant properties of flavonoids may contribute to their neuroprotective effects¹².

 

Flavonoids, recognised as crucial phytoconstituents, exert a noteworthy influence on biological activities in humans. In this study, we retrieved thirteen recently deposited flavonoids from PubChem, and assessed their potential to inhibit MAO-B using molecular docking techniques and in silico parameter assessments.

 

MATERIALS AND METHODS:

In silico Platform:

Schrödinger 2023-1, LLC, New York's Maestro13.5.128 version was used to perform the docking studies and QikProp (to evaluate the physicochemical and ADMET properties). The workstation machine has an Intel Core i7 processor, 16GB of RAM, and a 64-bit operating system. It runs Linux-x86_64 as its operating system. The other online software programs like the Molinspiration cheminformatics tool were utilised to predict the bioactivity scores and toxicity profiles were evaluated using ProTox- II

 

Ligand preparation:

Ligand structures of recently deposited flavonoids were retrieved from PubChem in SMILES format, drawn using ChemDraw, and imported into Schrödinger's Maestro interface. LigPrep was used to generate 3D structures at pH 7, applying the OPLS-3 force field for energy minimization and low-energy conformations¹³.

 

Physicochemical, ADMET properties and bioactivity prediction:

Physicochemical properties and pharmacokinetic properties of the ligands were determined using the QikProp module of Schrödinger^14,15. The toxicity parameters were predicted using ProTox-II16 and bioactivity score were determined using Molinspiration¹⁶.

 

Molecular docking and Prime MM-GBSA binding free energy:

Molecular docking of 21 flavonoids against MAO-A (2Z5X) and MAO-B (2V5Z) was performed using XP docking, considering the lowest binding energy as the best conformation^17,18. The Prime MM-GBSA calculated binding free energy (ΔGbind) using molecular mechanics and solvation models¹⁹.

 

RESULT AND DISCUSSION:

Using the QikProp module, the physicochemical properties of flavonoids were evaluated to assess drug-likeness and adherence to RO5²⁰. Table 1 presents these properties. According to RO5, drug-like molecules should have a molecular weight below 500 Da, logP ≤ 5, HB donors ≤ 5, and HB acceptors ≤ 10. All flavonoids followed RO5 with fewer than four violations, indicating drug-like potential.

 

Most flavonoids had molecular weights below 500 Da, except amorphin, elatin, and isosaponarin. The QPlogPo/w values were within the acceptable range (-2.0 to 6.5). However, amorphin, elatin, isosaponarin, and genistein 8-C-glucoside showed violations to HB donor and acceptor values exceeding limits. Molecular volumes were within the specified range, and PSA values were within limits except for amorphin, elatin, and isosaponarin.

 

ADME Prediction:

Assessing pharmacokinetic parameters is crucial for understanding drug interactions and effects. Table 2 illustrates the ADME properties and their acceptable ranges.

 

Table 1: Physicochemical properties of flavonoids

Flavonoids	MW	HBD	HBA	QPlogo/w	SASA	FOSA	FISA	RO5	RO3
Acceptable range	≤500	≤5	≤10	-2.0 to 6.5	300-1000	0.0-750	7.0-330	< 4	< 3
Amorphin	704.68	6.00	22.75	-0.16	837.83	544.75	172.08	3	1
Laurifolin	356.37	2.00	5.70	2.57	612.12	226.84	181.74	0	0
Elatin	594.52	10.00	19.80	-2.59	797.96	242.84	413.79	3	2
Artocarpin	346.33	1.00	5.50	2.74	595.52	242.46	129.23	0	1
Hispidone	436.50	2.00	4.50	5.32	793.18	322.06	145.90	1	2
Eupatoretin	374.34	2.00	7.00	2.43	615.63	236.67	129.60	0	0
Eupatin	360.32	2.00	6.00	2.21	600.10	330.04	173.05	0	0
Ternatin	374.34	1.00	6.00	2.70	585.32	266.68	140.12	0	0
Isosaponarin	594.52	9.00	20.75	-2.55	874.95	305.11	423.62	3	2
Galangin	270.24	2.00	3.75	1.79	493.96	0.00	184.27	0	0
Genistein 8-C-glucoside	432.38	6.00	12.25	-0.64	667.84	0.00	327.72	1	2
Lanceolatin A	336.38	1.00	4.00	4.42	633.97	104.07	84.42	0	1

MW-Molecular Weight, HBD- Hydrogen Bond Donor, HBA- Hydrogen Bond Acceptor, QPlogo/w- Partition Co-efficient, SASA- Solvent Accessible Surface Area, FOSA- Hydrophobic component of the SASA, FISA- Hydrophilic component of the SASA, RO5- Rule of Five, RO3- Rule of Three.

 

Table 2: ADME properties of flavonoids

Flavonoids	%HOA	QPlogCaco	QPlogBB	CNS	QPlogKhsa	#metab	QPlogHERG
Acceptable range	>80% High <25% Low	>500 Great <25 Poor	–3.0 to 1.2	-2 to +2	-1.5 to1.5	1-8	Below –5
Amorphin	29.39	231.20	-1.95	-2	-1.204	12	-4.64
Laurifolin	82.70	187.26	-1.35	-2	0.323	6	-5.16
Elatin	0.00	1.18	-4.43	-2	-1.198	15	-5.38
Artocarpin	92.62	589.36	-0.98	-1	0.160	7	-4.94
Hispidone	91.92	409.54	-1.55	-2	1.172	10	-6.13
Eupatoretin	90.72	584.57	-1.03	-2	0.000	6	-4.94
Eupatin	82.07	226.35	-1.47	-2	0.040	6	-5.03
Ternatin	90.49	464.57	-1.04	-2	0.124	6	-4.39
Isosaponarin	0.00	0.95	-5.19	-2	-1.442	12	-6.47
Galangin	77.71	177.20	-1.28	-2	-0.029	3	-5.28
Genistein 8-C-glucoside	26.10	7.72	-3.24	-2	-0.720	9	-5.61
Lanceolatin A	100.00	1567.72	-0.50	0	0.727	2	-5.83

%HOA- Percent Human Oral Absorption, QPlogCaco- Caco-2 cell permeability, QPlogBB- Predicted brain/blood partition co-efficient, CNS- Predicted CNS activity, QPlogKhsa- Prediction of binding to human serum albumin, #metab- Number of likely metabolic reaction, QPlogHERG- Predicted IC50 value for blockage of HERG K+ Channels.

 

The bioavailability of the flavonoids was assessed based on aqueous solubility (logS), human oral absorption, and compliance with Jorgensen's Rule of Three (RO3), where compounds meeting at least two criteria (logS > -5.7, Caco-2 > 22nm/s, and primary metabolites < 7) are more likely to be orally available²¹. Most compounds met the solubility range, except for hispidone and lanceolatin A. Gut–blood barrier permeability was assessed using Caco-2 values, showing high permeability (>500) for atrocarpin, eupatoretin, and lanceolatin A, while elatin, isosaponarin, and genistein 8-C-glucoside had poor permeability (<25). Human oral absorption was > 80% for laurifolin, artocarpin, hispidone, eupatoretin, eupatin, ternatin, and lanceolatin A. Elatin and isosaponarin showed <25% absorption. Blood-brain barrier (BBB) penetration was predicted using blood–brain partition coefficients (logBB), with elatin, isosaponarin, and genistein 8-C-glucoside showing limited BBB penetration²². Metabolic reactions (#metab) were predicted for the compounds, with amorphin, elatin, hispidone, isosaponarin, and genistein 8-C-glucoside exceeding the specified range of 1–8 reactions due to their molecular complexity²³. Blockage of the HERG K+ channel was also assessed, with amorphin, artocarpin, eupatoretin, and ternatin predicted to have potential cardiac toxicity²⁴. Finally, solvent-accessible surface area (SASA), FOSA, and FISA were evaluated²⁵, with all compounds satisfying the SASA and FOSA limits, while elatin and isosaponarin were out of the acceptable FISA range.

 

Bioactivity prediction:

The Molinspiration tool was employed to forecast the bioactivity score of flavonoids. A molecule is deemed biologically active if its bioactivity score exceeds 0.00. Scores falling between -0.50 and 0.00 are categorized as moderately active, while a score below -0.50 indicates potential inactivity²⁶. The bioactivity score of the flavonoids is detailed in Table 3.

 

G protein-coupled receptors (GPCRs) modulate dopamine and serotonin neurotransmission, playing a key role in neurodegenerative disorders (NDDs)²⁷. Most flavonoids showed moderate to good GPCR bioactivity scores. Ion channel modulators regulate ion flow across membranes, influencing neuronal excitability²⁸. Except for amorphin, flavonoids exhibited moderate to good ion channel activity. Kinase inhibitors prevent neuronal cell death and reduce neuroinflammation²⁹. Amorphin was inactive, with bioactivity scores below -5.0. Nuclear receptors regulate gene expression related to inflammation, oxidative stress, and neuronal survival³⁰.

 

Table 3: Bioactivity prediction of flavonoids

Flavonoids	GPCR ligand	Ion channel modulator	Kinase inhibitor	Nuclear Receptor ligand	Protease inhibitor	Enzyme inhibitor
Amorphin	-0.49	-1.54	-1.29	-1.20	-0.45	-0.47
Laurifolin	0.27	0.12	-0.18	0.76	0.27	0.50
Elatin	0.02	-0.43	-0.06	-0.09	0.01	0.21
Artocarpin	0.04	-0.11	-0.03	0.50	-0.17	0.32
Hispidone	0.03	-0.24	-0.21	0.28	-0.06	0.12
Eupatoretin	-0.10	-0.21	0.17	0.14	-0.26	0.16
Eupatin	-0.14	-0.33	0.20	0.09	-0.34	0.14
Ternatin	-0.15	-0.08	0.10	0.02	-0.28	0.17
Isosaponarin	0.04	-0.39	-0.10	-0.05	0.01	0.25
Galangin	-0.13	-0.21	0.19	0.28	-0.32	0.28
Genistein 8-C-glucoside	0.03	-0.43	0.03	0.16	-0.25	0.37
Lanceolatin A	0.11	-0.28	0.10	0.41	-0.14	0.24

Table 4: Toxicity prediction of flavonoids

Sl. No	Flavonoids	Predicted LD50 (mg/kg)	Predicted toxicity class	Carcinogenicity		Mutagenicity
				probability	activity	probability	activity
1.	Amorphin	3	1	Inactive	0.80	Inactive	0.59
2.	Laurifolin	2000	4	Inactive	0.63	Inactive	0.62
3.	Elatin	1213	4	Inactive	0.78	Inactive	0.51
4.	Artocarpin	1190	4	Inactive	0.62	Inactive	0.97
5.	Hispidone	4000	5	Inactive	0.66	Inactive	0.68
6.	Eupatoretin	5000	5	Inactive	0.63	Inactive	0.77
7.	Eupatin	5000	5	Inactive	0.57	Inactive	0.85
8.	Ternatin	5000	5	Inactive	0.63	Inactive	0.77
9.	Isosaponarin	5000	5	Inactive	0.84	Inactive	0.74
10.	Galangin	3919	5	Inactive	0.72	Inactive	0.52
11.	Genistein 8-C-glucoside	832	4	Inactive	0.72	Active	0.52
12.	Lanceolatin A	2570	5	Active	0.54	Inactive	0.56

 

 

Amorphin showed inactivity (-1.20). Protease inhibitors help clear misfolded proteins, preventing toxic accumulation³¹. All flavonoids showed moderate to good enzyme inhibitor activity, which is crucial in modulating neurotransmitter levels and restoring balance in NDDs.

 

Toxicity Prediction:

The in silico toxicity of the compounds was found using two online tools and given in Table 4.  Lethal dose (LD₅₀), toxicity class, carcinogenicity, and mutagenicity were found using ProTox-II online software³³.

 

The globally standardized LD₅₀ classification system identifies compounds with an LD₅₀ ≤ 50mg/kg as highly toxic. Except for amorphin, all compounds exceeded this threshold, classifying them as non-toxic, while amorphin, with an LD₅₀ of 3 mg/kg, is highly toxic. Regarding toxicity class, amorphin is classified as Class I (highly toxic), while laurifolin, elatin, artocarpin, and genistein 8-C-glucoside are in Class IV, and the remaining compounds fall under Class V, indicating lower toxicity. For carcinogenicity, lanceolatin A showed active carcinogenicity with a probability of 0.54, while the other flavonoids were inactive, with probabilities ranging from 0.53 to 0.84. In terms of mutagenicity, genistein 8-C-glucoside displayed active mutagenicity (probability 0.51), while all other compounds were inactive, with probabilities ranging from 0.51 to 0.97.

 

Molecular Docking:

Molecular docking determines how the ligand and target protein interact. The docking score and interaction of each compound with 2V5Z and 2Z5X are illustrated in Table 5.

 

Table 5: Docking score and interaction of flavonoids with target 2V5Z and 2V5X 

Flavonoids	PDB	Docking score (kcal/mol)	H bond	Hydrophobic interaction	Pi-Pi Stacking
Amorphin	2V5Z	-	-	-	-
	2Z5X	-	-	-	-
Laurifolin	2V5Z	-12.170	Tyr 326, Tyr 188, Cys 172	Tyr 398, Tyr 326, Ile 199, Ile 198, Phe 168, Leu 171, Cys 172, Val 173, Tyr 188, Tyr 435, Met 436, Phe 343, Tyr 60	Tyr 398, Tyr 326
	2Z5X	-11.62	Tyr 69, Tyr 197	Met 445, Tyr 444, Tyr 197, Ile 207, Ile 180, Cys 323, Leu 337, Ile 335, Met 350, Phe 352, Tyr 407, Cys 406, Tyr 69, Ala 68	Tyr 444, Tyr 407, Phe 352
Elatin	2V5Z	-	-	-	-
	2Z5X	-	-	-	-
Artocarpin	2V5Z	-11.75	Gly 57	Tyr 60, Tyr 398, Leu 328, Tyr 326, Ile 198, Ile 199, Leu 167, Phe 168, Leu 171, Cys 172, Tyr 188, Ile 316, Trp 119, Tyr 435, Met 436, Phe 343	Tyr 60, Tyr 398
	2Z5X	-4.10	Tyr 444, Asn 181	Tyr 407, Met 445, Tyr 444, Tyr 197, Ile 180, Ile 207, Phe 208, Val 210, Ile 325, Cys 325, Cys 323, Ala 111, Leu 97, Ile 335, Leu 337, Met 350, Phe 352, Tyr 69, Ala 68	Phe 352
Hispidone	2V5Z	-10.36	Ser 59, Gly 434, Tyr 188	Tyr 60, Tyr 326, Leu 328, Phe 343, Phe 168, Ile 199, Ile 198, Leu 171, Cys 172, Tyr 188, Tyr 398, Tyr 435, Met 436	Tyr 435, Tyr 326
	2Z5X	-10.89	Met 445, Tyr 69	Met 445, Tyr 69, Tyr 444, Ala 68, Tyr 407, Cys 406, Ile 180, Phe 208, Ile 335, Leu 337, Met 350, Phe 352,	Tyr 444, Tyr 407
Eupatoretin	2V5Z	-10.05	Tyr 188	Tyr 60, Tyr 398, Tyr 326, Ile 316, Phe 168, Leu 171, Cys 172, Ile 198, Ile 199, Tyr 188, Tyr 435, Met 436, Phe 343	Tyr 398, Tyr 326
	2Z5X	-10.70	Phe 208, Asn 181	Met 445, Tyr 444, Tyr 406, Tyr 197, Ile 180, Ile 207, Phe 208, Val 210, Leu 97, Cys 323, Ile 325, Leu 337, Met 335, Phe 352, Met 350, Tyr 69, Ala 68	Tyr 407
Eupatin	2V5Z	-11.00	Cys 172, Tyr 188, Ser 59, Tyr 60	Tyr 60, Tyr 398, Tyr 326, Ile 199, Ile 198, Phe 168, Leu 171, Cys 172, Tyr 188, Tyr 435, Phe 343	Tyr 398
	2Z5X	-11.48	Asn 181, Phe 208	Met 445, Tyr 444, Tyr 197, Ile 180, Ile 207, Phe 208, Val 210, Leu 97, Cys 323, Leu 337, Ile 335, Tyr 407, Tyr 69, Ala 68, Phe 352, Met 350, Ala 68	Tyr 407
Ternatin	2V5Z	-10.26	Tyr 188, Lys 296	Tyr 60, Cys 397, Tyr 398, Tyr 326, Phe 168, Leu 171, Cys 172, Ile 199, Ile 198, Tyr 188, Phe 343, Tyr 435	Phe 343, Tyr 398
	2Z5X	-10.53	Gly 443	Met 445, Tyr 444, Tyr 197, Tyr 407, Ile 180, Ile 207, Phe 208, Ile 335, Leu 337, Met 350, Phe 352, Cys 323, Ala 68, Tyr 69	Tyr 444, Tyr 407,
Isosaponarin	2V5Z	-16.79	Ser 59, Met 436, Pro 102, Tyr 188	Cys 172, Leu 171, Phe 168, Leu 167, Leu 164, Trp 119, Ile 316, Pro 104, Phe 103, Pro 102, Phe 99, Tyr 326, Ile 198, Ile 119, Leu 88, Tyr 188, Phe 343, Tyr 60, Met 436, Tyr 435, Tyr 398	Tyr 398, Tyr 326
	2Z5X	-	-	-	-
Galangin	2V5Z	-10.44	Tyr 188, Cys 172, Ser 59	Phe 343, Tyr 326, Phe 168, Leu 171, Cys 172, Val 173, Tyr 398, Tyr 188, Tyr 60, Tyr 435, Ile 199, Ile 198	Tyr 435
	2Z5X	-10.15	Asn 181	Tyr 444, Tyr 197, Ile 180, Ile 207, Phe 208, Val 210, Cys 323, Leu 337, Met 350, Ile 335, Tyr 407, Phe 352, Tyr 69, Ala 68	Phe 208, Tyr 407
Genistein 8-C-glucoside	2V5Z	-15.81	Lys 296, Tyr 188, Cys 172, Gly 434	Tyr 60, Phe 343, Tyr 326, Phe 168, Leu 171, Cys 172, Val 173, Ile 199, Ile 198, Tyr 188, Tyr 435, Tyr 398, Cys 397	Tyr 398, Tyr 435, Tyr 326
	2Z5X	-13.39	Asn 181, Ala 68	Val 303, Met 445, Tyr 444, Cys 406, Tyr 407, Tyr 197, Ile 180, Ile 207, Phe 208, Val 210, Cys 323, Leu 337, Ile 335, Met 350, Phe 352, Tyr 69, Ala 68	Tyr 407
Lanceolatin A	2V5Z	-8.09	Lys 296, Tyr 188	Tyr 60, Phe 343, Met 341, Tyr 326, Leu 171, Cys 172, Tyr 398, Cys 397, Tyr 188, Tyr 435, Met 436	Tyr 398, Tyr 435
	2Z5X	-4.98	Gln 215	Cys 406, Tyr 407, Trp 397, Met 445, Tyr 444, Ile 180, Val 70, Tyr 69, Ala 68, Val 65, Met 350, Phe 352, Val 303	Phe 352, Trp 397, Tyr 444

 

Binding with 2V5Z:

Isosaponarin and genistein 8-C-glucoside exhibited the most favorable docking scores of -16.79 and -15.81 kcal/mol, respectively, surpassing safinamide’s score of -12.26 kcal/mol. Safinamide formed a hydrogen bond with Gln 206 and engaged in polar interactions with Ser 59, Gln 65, and Gln 206, along with hydrophobic interactions with multiple residues.

 

Isosaponarin formed four hydrogen bonds with Tyr 188, Ser 59, Met 436, and Pro 102, along with pi-pi stacking with Tyr 398 and Tyr 326 (Fig. 1). Hydrophobic interactions were observed with numerous residues, including Leu 164, Trp 119, and others.

 

Genistein 8-C-glucoside formed four hydrogen bonds with Lys 296, Tyr 188, Cys 172, and Gly 434 (Fig. 2), and engaged in polar interactions with Ser 59 and Gln 206. It also exhibited hydrophobic interactions with various residues and aromatic pi-pi stacking with Tyr 326 and Tyr 398. These interactions likely contribute to the higher binding affinity of these compounds compared to the co-crystal.

 

 

Fig. 1: a) 2D and b) 3D interactions of the isosaponarin with 2V5Z

 

 

Fig. 2: a) 2D and b) 3D interactions of the genistein 8-C-glucoside with 2V5Z

 

Binding with 2Z5X:

The co-crystal harmine achieved a docking score of 6.683kcal/mol, interacting hydrophobically with residues Tyr 197, Tyr 444, Tyr 407, Ile 180, Ile 207, Phe 208, Ile 335, Phe 352, Met 350, Tyr 69, and Ala 68. Polar interactions were with Asn 181 and Gln 215, while pi-pi stacking occurred with Tyr 407. Genistein 8-C-glucoside exhibited the highest docking score of -13.39 kcal/mol, forming hydrogen bonds with Asn 181 and Ala 68, and engaging in pi-pi interactions with Tyr 407 (Fig. 3). Hydrophobic interactions were observed with multiple residues including Tyr 444, Cys 406, and Tyr 407. Polar interactions occurred with Ser 59 and Gln 206. Laurifolin obtained a docking score of -11.62 kcal/mol, forming hydrogen bonds with Tyr 69 and Tyr 197 (Fig. 4). Hydrophobic interactions were observed with Tyr 444, Tyr 197, and other residues. Aromatic pi-pi stacking occurred with Tyr 444, Tyr 407, and Phe 352. Both genistein 8-C-glucoside and laurifolin exhibited hydrogen bonding, which may contribute to their higher docking scores compared to the co-crystal

 

MMGBSA binding free energy:

The MM-GBSA approach determined the receptor-ligand binding energy. Key energy contributors include ΔG bind, ΔG coulomb, ΔG covalent, ΔG Hbond, ΔG lipophilic, ΔG solvent GB, and ΔG van der Waals, detailed in Table 6. Binding free energy (ΔG bind) ranged from -29.01 to -82.73 kcal/mol for 2V5Z and -18.84 to -86.83kcal/mol for 2Z5X. While ΔG covalent and ΔG solvent GB were unfavourable, ΔG coulomb, ΔG Hbond, ΔG lipophilic, and ΔG van der Waals contributed favourably to flavonoid binding.

 

 

 

 

Fig. 3: a) 2D and b) 3D interactions of the genistein 8-C-glucoside with 2Z5X

 

Fig. 4: a) 2D and b) 3D interactions of the laurifolin with 2Z5X

Table 6: MMGBSA binding free energy calculation

Flavonoids	PDB	ΔG bind	ΔG coulomb	ΔG covalent	ΔG Hbond	ΔG lipo	ΔG Solvent GB	ΔG vdW
Amorphin	2V5Z	-	-	-	-	-	-	-
	2Z5X	-	-	-	-	-	-	-
Laurifolin	2V5Z	-56.60	-18.20	11.18	-0.80	-45.11	36.80	-38.52
	2Z5X	-50.73	-21.58	10.89	-0.88	-46.16	45.76	-33.80
Elatin	2V5Z	-	-	-	-	-	-	-
	2Z5X	-	-	-	-	-	-	-
Artocarpin	2V5Z	-70.33	-17.82	22.33	-1.11	-70.56	40.52	-38.35
	2Z5X	-28.27	-7.35	16.03	-0.42	-71.79	49.50	-10.81
Hispidone	2V5Z	-66.34	-15.13	8.94	-0.63	-40.20	32.15	-47.27
	2Z5X	-62.36	-13.05	12.20	-0.50	-41.01	36.48	-54.41
Eupatoretin	2V5Z	-68.87	-13.43	2.66	-0.26	-40.14	37.41	-49.82
	2Z5X	-68.46	-9.73	6.54	-0.57	-42.61	42.17	-57.04
Eupatin	2V5Z	-71.63	-19.59	4.56	-0.81	-36.17	37.06	-51.40
	2Z5X	-67.62	-17.77	6.53	-0.75	-38.99	43.36	-53.02
Ternatin	2V5Z	-68.70	-13.75	5.40	-1.28	-39.96	27.13	-41.08
	2Z5X	-61.69	-7.04	7.02	-0.67	-42.82	35.30	-49.15
Isosaponarin	2V5Z	-82.73	-48.91	24.01	-0.96	-73.56	57.75	-38.19
	2Z5X	-	-	-	-	-	-	-
Galangin	2V5Z	-48.98	-13.52	3.42	-0.77	-25.45	33.82	-40.75
	2Z5X	-49.12	-10.06	1.13	-0.45	-27.18	36.87	-40.95
Genistein 8-C-glucoside	2V5Z	-67.77	-20.79	4.85	-1.38	-45.11	41.87	-42.05
	2Z5X	-43.61	-32.73	13.92	-0.86	-47.55	51.15	-20.75
Lanceolatin A	2V5Z	-49.09	-10.27	25.15	-0.77	-46.97	24.82	-37.57
	2Z5X	-31.34	-14.81	23.24	-0.24	-51.71	27.54	-13.99

ΔG bind- free energy of binding, ΔG Coulomb- Coulomb energy, ΔG covalent- covalent energy (internal energy), ΔG H Bond- hydrogen bonding energy, ΔG Lipophilic- hydrophobic energy (non-polar contribution estimated by solvent accessible surface, ΔG Solvent GB- electrostatic solvation, ΔG vdW - Van der Waals energy.

 

CONCLUSION:

Most of the flavonoids demonstrated activity against MAO-A and MAO-B targets, with moderate to good physicochemical, pharmacokinetic, and drug-likeness properties, and comparatively lower toxicity. Among the selected flavonoids, genistein 8-C-glucoside, exhibited promising inhibitory potential and high binding affinity to both targets, although it displayed low permeability across the BBB and CNS. Given their plant-derived origin, the intricate structures of these compounds pose a challenge. While flavonoids show potential in inhibiting MAO enzymes, it is crucial to recognise the need for further research to fully understand the specific mechanisms and clinical implications. Additionally, thorough investigations are required to enhance the lipophilicity of these compounds through structural modifications, thereby improving BBB and CNS permeability.

 

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Received on 05.07.2024      Revised on 19.12.2024 Accepted on 14.03.2025      Published on 05.09.2025 Available online from September 08, 2025 Research J. Pharmacy and Technology. 2025;18(9):4289-4296. DOI: 10.52711/0974-360X.2025.00616 © RJPT All right reserved
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